Welded portal frame connections

[IH1980]

Hi all,

Hopefully someone can help me (or confirm what I already think i know). I am running an assessment on an existing steel portal which has been taken down and is being erected in a new location. The apex and the eaves, rather than being bolted, are welded like the image below - there is a small haunch on the apex and nothing on the eaves. There is then a splice about 2.5m away from the eaves on each side, so the frame is in 3 pieces, 2 Cols with a 2.5m long 'stub' rafter and a pair of welded rafters. Hope that all makes sense.

Now if I assume the connection welds are full strength butt welds then great, I know that I can achieve the full section strength in bending. But i still need to consider local effects like column web crushing/bearing etc due to the crank won't I? I have only ever run these connections in software as bolted, so want to make sure before i have to dive into the books to look up all the checks!

EDIT: perhaps i wasn't clear on something - the eaves is not a rafter to column flange weld - both sections are cut to the angle and welded all round. So the TF of the rafter is welded to the outside flange of the column, BF of rafter to the inside flange of the column, and web to web. Like the apex but on a more severe angle (its 17 degree pitch).

 

[BAretired]

I would have expected a stiffener plate at the eave connection. Without that, you will not achieve the full strength of the section in bending, even with a full strength weld.

BA

 

[robyengIT]

 

[IH1980]

Apologies for going missing on my own thread, got dragged into fighting a different fire as you do. Can't believe I didnt think to check Blodgett, i even used it for something else this week. I'll start there - amazingly a second instance of this has come up this week, what are the chances..

 

[dik]

Surprised there are no stiffeners at the ridge...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[IH1980]

Yes - having read what Blodgett has to say on it, i think i will be asking them to weld up a diagonal stiffener across the eaves mitre line and a vertical one at the apex. After all they'll be grinding off the existing cleats for the rails to weld new ones on so it shouldnt be a big deal.

 

[Agent666]

Yeah agree, best to weld some correctly sized stiffeners. At eave, I've never been convinced of the single diagonal stiffener arrangement in terms of the restrain it offers to members as one of the column flanges obviously is not continuous to the top of the beam. In combination with horizontal stiffeners they work quite well instead of requiring doubler plates for the panel zone. But as a single diagonal stiffener I've never been that convinced of their effectiveness, but having said that people seem to use them.

I like how they just painted what someone could see from the ground (web and underside of flanges... have to watch out for that one in the future with the more dodgy contractors round these parts .....

https://engineervsheep.com

 

[dik]

These are normally not for flexure, but to provide stiffeners for compression buckling from shear... You still need the continuation of the flange material... generally.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik